There have been conventionally proposed detection devices that detect a detection object. For example, a detection device disclosed in JP H8-014889 A acquires a light reception quantity of reflection light of light projected by the detection device, and a distance between the detection device and the detection object. It is proposed that the detection device sets one of a first mode of detecting a detection object by using the light reception quantity and by not using the distance, and a second mode of detecting a detection object by using the distance and by not using the light reception quantity.
As described above, the detection device described in JP H8-014889 A detects a detection object by using one of the light reception quantity and the distance and by not using the other of the light reception quantity and the distance, when any one of the first mode and the second mode is selected. Therefore, in the situation where a detection object cannot be detected when only the light reception quantity is used, or in the situation where a detection object cannot be detected when only the distance is used, there has been a problem that a detection object cannot be properly detected.